Nicotine-type acetylcholine receptors (nAChRs) are expressed on pre- as well as post synaptic structures within the vertebrate central and peripheral nervous systems as well as being widely distributed in invertebrate systems. There is considerable diversity in neuronal nAChR subtypes evident in distinct biophysical and pharmacological profiles that likely reflect differences in nAChR subunit composition. Our previous studies have elucidated two unusual subsets of nAChRs. The first, in vertebrates, is a pre synaptic nAChR that is gated by minute amounts of nicotine and mediates an alpha-bungarotoxin-sensitive facilitation of synaptic transmission, requiring Ca influx through this ionotropic receptor. The second, in this invertebrate, Aplysia californica, is also activated by nicotine blocked by alpha-bungarotoxin and appears to mediate a previously unrecognized slow chloride current in identified neurons. Using a combination of biochemical and electrophysiological methods, we will investigate the role of arachidonic acid metabolism as a signaling pathway in relation to both receptor subtypes and evaluate the functional consequences of these biologically active lipids in neuronal activity. We will address three specific aims: 1) What is the role of lipid metabolites in pre synaptic facilitation by nicotine in vertebrates? 2) What are the roles of the lipoxygenase pathways in neural signaling in Aplysia? 3) How closely related are the 8- and 12-lipoxygenases? Where are they located? Do both exist in invertebrate neurons? Do both exist in vertebrate neurons? In view of the emergent role of specific lipid metabolites in synaptic plasticity, the proposed studies should provide important insights into the molecular mechanisms of eicosanoid action by analyzing excitability at well characterized interneuronal synapses.